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The effect of cold working on the aging behaviors and mechanical Properties of the Al-2Li-3Cu-0.12Zr alloy have been studied. This results show that the formation of T₁ and θ′ phases are accelerated by introduction of 5% cold rolling after as-quenched state two step aging treatment is most effective in aging response and impact energy increase among tested conditions. This results are attributed to the two step aging treatment which has the more dense and homogeneous distribution of strengthening phases such as T₁ and θ′. It is thought to be due to the participation of lithium to the formation of T₁ phase in early stage of aging treatment.

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The SiC powder was prepared by a SHS process using SiO₂, Mg and C as raw materials to determine the optimum process variables. The results obtained from this study may be summarized as follows; 1) The mole ratio between C and Mg affected the magnesiothermic reduction reaction most and the highest yield of SiC was obtained at the mole ratio of SiO₂ : Mg : C = 1.0 : 2.5 : 2.2. 2) The propagation speed of combustion reaction was about l0㎜/sec increasing with the decrease of SiO₂ particle size. 3) The amount of unreacted silicon decreased with increasing compaction pressure. 4) Impurities were found to decrease by evaporation during the high temperature reaction or by solution during leaching process. 5) The particle size of prepared SiC powders was in the range of 0.2∼1.0 microns with the purity of about 98.885 weight percent.

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The changes of microstructures and mechanical properties of Al-Li-Cu-Mg-Zr P/M alloy with various composition and extrusion variables were observed. Increasing Li content, yield stress increases but tensile stress decreases because of increasing intermetallic phases and δ phase formation. As the extrusion temperature get higher from 573K to 773K, the larger size of subgrain is obtained. Besides in case of extrustion at 773K, composite precipitates are precipitated in the matrix. The mechanical properties of extruded bars-Y.S. (570MPa), E.L. (2.6%)-were obtained by the finer microstructure. The reason is considered that composite precipitates derived cross slip or Orowan by pass of dislocation and Zr acted as grain refiner to suppress recrystallization.

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Spalled oxide particles and corrosion products released from the surface of steam generator materials cause various problems of accelerating stress corrosion cracking, denting, wastage, erosion of turbine, and decrease of thermal efficiency. Because the major part of exposed material surface in steam generator atmosphere is the surface of the steam generator tube, it is important to know the oxidation behavior of the tube material. The oxidation behavior of three kinds of Inconel alloys, i.e., Inconel 600, Inconel 690 and Incoloy 800 in air, pure water, and steam was studied and the oxide layers were analysed by SEM, EDX, X-ray diffractometer. And thermal diffusivities of Inconel alloys were measured by the laser flash method. Inconel 690 shows the best resistance to oxidation among the three alloys tested in static air, pure water, and steam. The good oxidation resistance of Inconel 690 is due to maintaining uniform Cr₂O₃ layer during the oxidation time. The thermal diffusivity decreases as the extent of oxidation increases. The thermal diffusivity of Inconel 600 oxidized at 500℃ for 3hours in static air decreases to 85% of that of non-oxidized specimen. The results of this study can be applied to the development of oxidation resistant materials of controlled Cr content. And the test data can be used as reference for the estimation of the amount of sludge, and as input data of steam generator design.

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The grain growth of β region and the microstructural alteration of α phase depending on the various solution treatments have been studied in Ti-6Al-4V alloy. In specimens solutionized in β region, the grain size of β phase increase with increasing the temperature and the holding time. The hardness also increased with increasing temperature, but was nearly constant with increasing holding time, regardless of the grain size of β phase over 0.7㎜. In the specimens solutionzed in α+β region, as the solutionized temperature increased, the volume fraction of primary α phase and the vanadium content in α phase and α′+β phase decreased linearly. This seems to cause the decreasing hardness with increasing temperature. The Ms temperature of the specimen solutionized to vary matrix stucture has been shown to decrease about 25℃ than in the specimen of solution treated to vary volume fraction of β phase.

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AZ91 magnesium alloy machined chips were hot extruded at 300∼380℃ temperature range under the extrusion ratio of 25 : 1 and die angle(2θ) of 60˚. The microstructure and mechanical properties of the extruded chips were studied in order to find good extrusion properties. As-received ingot and extruded ingot were used as reference materials. Also, heat-treatment was carried out for all the extruded bars. The microstructure of the extruded chips showed fine equiaxed grains due to dynamic recrystallization during hot extrusion and the chips were perfectly bonded. The age-hardening behaviors of the extruded chips and the extruded ingot showed the highest peak of hardness at aging time of 26∼40 hours at 170℃. The tensile strength and elongation of the extruded chips at room temperature were 330 MPa and 10%, respectively. These value were approximately the same as those of the extruded ingot. In the effect of heat-treatment, the elongation of heat-treated extruded bars was founded to be less than that of as-extruded bars. This may be due to the grain-coarsening induced to softening during solution treatment.

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Reducing a surface roughness of hot-rolled stainless steel is essential to improve a buffing quality of cold-rolled stainless steel. Even though steel shot blasting increases the surface roughness (R_(max) value) of hot-rolled and annealed stainless steel, it is the most effective process for descaling. In order to improve the surface quality, the shot mark depth generated on the surface by shot blasting should be predicted and controlled. The relationship among the initial shot blasting velocity, shot size, blasting distance, blasting angle as well as shot mark depth was estabilished by a regression method. The results are in good agreement with the experimental results. This regression method could be applicable to other materials.

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DLC(Diamondlike carbon) thin films were obtained by PECVD(Plasma Enhanced Chemical Vapor Deposition) with CH₄ gas as a source gas and effects of preparation conditions on the optical band gap were studied. In case of PECVD of DLC thin films, it turned out that chemical vapor deposition and sputtering by physical collisions of reactive ion species occured simultaneously during deposition and thus the hydrogen concentration in the DLC thin films, which is known to influence directly on the optical band gap could be controlled by changing the energy of reactive ion species in the plasma. It was possible in this work to obtain different optical band gap of DLC thin films from 2.2eV to 0.6eV and make suitable explanations about the relationship between preparation conditions and optical band gap.

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The damping behavior of ferromagnetic Fe-Al-Mn alloy was investigated. The effect of aluminium content and heat treatment on the specific damping capacity(SDC) of alloys was studied over a range of Al 3-13wt.%. After heated at 1000℃ for 40 minutes in a vacuum furnace, alloys were cooled by three different ways; furnace cooling, air cooling and water quenching. By the results of X-ray and neutron diffraction test, the relations between the crystal structure and the magnetic structure were clarified. The average domain size by neutron diffraction showed the minimum value of 10.5㎛ at 5.5% Al content. SDC results showed that SDC_(max) reached its highest value of 35% at a range of 5-6wt.%Al. On the basis of the data obtained by analyzing magnetic hysteresis loops and neutron scattering method, it was found that alloys subjected to furanace cooling and air cooling had higher SDC_(max) than that of water quenched one, because they had more volume of 90˚ magnetic domain. Compared with the furnace cooled alloy, the air cooled one showed higher SDC_(max) value, because it had not short range order.

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Numerical simulation for copper single crystal growth by a heat exchanger method has been performed including the effects of fluid flow, conduction and radiation heat transfer using the actual geometry of growing furnace. The finite difference method based on a control volume approach and SIMPLE algorithm were used to solve the momentum and energy equations. Almost all parts of the furnace including heater, insulating materials and crucible were considered in the calculation domain and the latent heat was also accounted by an iterative heat evolution method. The effects of cooling rate of heater and crucible position and melt weight were investigated together with the role of natural convection in melt. The optimum process conditions for single crystal growth were determined. The calculated results of critical cooling rate, solidification time and the critical ratio of the height to the radius of crystal were found to be in a good agreement with the experimental results.

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